Abstract：The information of strata such as P-and S-wave velocities and density is contained in prestack seismic data. Using prestack seismic inversion to acquire the information in seismic data is able to reveal the nature of lithology and pore fluid. Taking the relationship between seismic CRP gather data and strata parameters formed by plane waves propagating in layered elastic half-space,the paper presented prestack three-term inversion based on Powell's conjugate direction substitution. Without requiring solution and storage of large and complicated first-and second-order derivative,the method greatly improved the ill-conditioned problem of three-term inversion by normalization of objective function,and compressed the solution space as well. The usage of new substitution strategy in direction substitution process effectively prevented the linear correlation in searching direction. At the same time,the split inversion strategy for low and high frequencies was presented in implementing the inversion,which both guarantees the stability and precision of inverted results when prestack seismic data are lower S/N ratio and greatly improved convergent speed. The method has been tested with theoretical model and used in practical work zone of oilfield,laid the foundation for lithologic recognition and favorable reservoir prediction by fully using prestack seismic data.
